In general, PDP comprises two opposed glass substrates, a pair of electrodes systematically arranged in the glass substrates, and a gas (mainly Ne or the like) sealed therebetween. A voltage is applied across the electrodes to produce discharge within minute cells around the electrodes to emit light from each cell, thereby displaying information. Systematically arranged cells are selectively subjected to discharge luminescence in order to display information. Such PDPs are classified into two types, a direct current type PDP, wherein electrodes are exposed to a discharge space (DC type), and an alternating current type (AC type) wherein electrodes are covered with an insulating layer. Each of these types is further classified into a refresh drive system and a memory drive system according to display functions and memory drive systems.
FIG. 1 is an embodiment of the construction of an AC type PDP. In the drawing, a front plate 1 and a back plate 2 are shown separately from each other. As shown in the drawing, the glass front plate 1 and the back plate 2 are arranged parallel and opposite to each other. Barrier ribs 3 are provided so as to stand in a fixed state on the back plate 2 in its front surface side, and the front plate 1 and the back plate 2 are held while leaving a given distance between the front plate 1 and the back plate 2 by means of the barrier ribs 3. Composite electrodes each comprising a sustaining electrode 4 as a transparent electrode and a bus electrode 5 as a metallic electrode are provided parallel to each other on the front plate 1 in its back plate side, and a dielectric layer 6 is provided so as to cover the composite electrode. Further, a protective layer 7 (MgO layer) is provided on the surface of the dielectric layer 6.
On the other hand, address electrodes 8 are provided between the barrier ribs 3 on the back plate 2 in its front surface side so that the address electrodes 8 are parallel to each other and orthogonal to the composite electrodes. Further, a fluorescent substance 9 is provided so as to cover the wall surface of the barrier ribs 3 and the bottom face of cells.
In the AC type PDP, a predetermined voltage is applied across the composite electrodes on the front plate 1 to create an electric field, thereby producing discharge in each cell as a display element defined by the front plate 1, the back plate 2, and the barrier ribs 3. Ultraviolet light produced by the discharge permits the fluorescent substance 9 to emit light, and light passed through the front plate 1 is viewed by an observer.
Use of a photoresist film comprising a fluorescent substance-containing photosensitive resin composition has been proposed for coating the fluorescent substance (see, for example, Japanese Patent Laid-Open Nos. 273925/1994, 95239/1996, and 95250/1996).
In this coating method, a photosensitive composition is pressed into cells formed in a back plate of PDP, the photosensitive composition is exposed and developed, followed by firing to burn off the organic material in the photosensitive composition, thereby forming a fluorescent substance layer on the surface of the cells. In this case, a satisfactorily large discharge space should be ensured in the cells after the firing, making it necessary to increase the content of the organic material in the photosensitive resin composition, that is, to lower the content of the fluorescent substance. This requires a large quantity of thermal energy and further poses an additional problem that the firing evolves a large amount of gas, rendering the control of the firing oven complicate.
Further, the above method involves a serious problem that, since the photosensitive resin composition pressed into the cells contains a large amount of the organic material, the photosensitive composition shrinks with the elapse of the firing time and the finally formed fluorescent substance layer lifts from the cell surface and does not come into intimate contact with the cell surface.
Accordingly, an object of the present invention is to solve the problems of the prior art and to provide a photoresist film which can form an even fluorescent substance layer in intimate contact with the cell surface through a simple process, and a back plate of PDP using the film.